While the laboratory macaque is the most appropriate animal model for studying early pregnancy events in the human, the lack of practical methods to monitor endocrine events in the periimplantation period of the monkey model has limited the use of this animal resource. The use of both a monkey chorionic gonadotropin (MCG) enzyme-linked immunosorbent assay (ELISA) and ultrasonography can now be used to detect and monitor normal and abnormal events as early as three days post implantation in macaque species. In order to validate the MCG elisa as a useful tool for detecting early pregnancy and early fetal loss, daily serum and urine will be measured from approximately ten pregnant animals. The elisa for MCG uses a monoclonal anti-bovine beta (518-b7) antibody for capture and a polyclonal anti-HCG antibody conjugated to horseradish peroxidase for signal. Ultrasonography will also be performed during the periimplantation period for identification of the physical changes in the endometrium and uterine cavity. Females will be hand-restrained on gd-12 through 15 and ultrasound examinations will be performed using an ultramark 9 with HDI~, ATL, inc. Currently, fourteen monkeys were bred to proven males and have had daily urines from cycle day (cd) 9 to gestation day (gd) 20 and peripheral bloods from gd 7-20 collected. Measurement of urinary estrone-conjugates was used to determine the day of ovulation, gd-0. Two pregnancies have been confirmed by ultrasound. Urinary and serum mcg will be performed at a later date. Preliminary data from archived pregnancy profiles from cynomolgus macaques (n=14), show detection of MCG as early as gd-11, (1/14), and gd-12 to gd-15 for the remaining 13 females evaluated. Detection of urinary mcg occurred 24 (n=2) and 48 hours (n=1) after serum mcg detection.